Gear unit and powertrain for a vehicle

ABSTRACT

A gear unit for a powertrain of a vehicle includes a stepped planetary gearset, a first gear shifting element and a second gear shifting element. The stepped planetary gearset has at least a first ring gear, a second ring gear and a plurality of stepped planet gears rotatably mounted at a first planet carrier. The first planet carrier drivingly connects to an electric machine. The second ring gear is connected to an output shaft of the gear unit so as to be fixed with respect to rotation relative to it. The first gear shifting element fixes the first ring gear relative to a housing in a closed state, and the second gear shifting element brings the stepped planetary gearset into direct drive in a closed state. One of the two gear shifting elements is in the closed state for driving the output shaft in rotation.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention is directed to a gear unit for a powertrain of an at leastpartially electrically driven vehicle. The invention is further directedto a powertrain comprising such a gear unit.

2. Description of the Related Art

A powertrain for a vehicle with at least one electric drive, which iscouplable with at least a first transmission ratio stage and a secondtransmission ratio stage via a driveshaft, is known from the publicationWO 2014/139 744 A1. At least one shifting device is provided forshifting the transmission ratio stages, this shifting device comprisingat least one positively engaging shifting element and at least onefrictionally engaging shifting element for carrying out power shifts.Each of the transmission ratio stages can be shifted with the positivelyengaging shifting element. At least one of the ratio stages can beshifted with the positively engaging shifting element as well as withthe frictionally engaging shifting element.

SUMMARY OF THE INVENTION

It is an object of the present invention to propose an alternativetwo-speed gear unit and an alternative powertrain with a two-speed gearunit. This object may be met according to a first aspect of theinvention by a gear unit for a powertrain of an at least partiallyelectrically driven vehicle which comprises a stepped planetary gearset,a first gear shifting element and a second gear shifting element. Thestepped planetary gearset has at least a first ring gear, a second ringgear and a plurality of stepped planet gears rotatably mounted on afirst planet carrier. The first planet carrier is configured to bedrivingly connected to an electric machine. The second ring gear isconnected to an output shaft of the gear unit so as to be fixed withrespect to rotation relative to it. The first gear shifting element isconfigured to fix the first ring gear relative to a housing in a closedstate. The second gear shifting element is configured to bring thestepped planetary gearset into direct drive in a closed state, and oneof the two gear shifting elements is in the closed state for driving theoutput shaft in rotation. A gear unit of this kind enables a two-speeddrive of the vehicle, and a ratio step of between 1.7 and 2.5,preferably a ratio step of approximately 2.0, is advantageously madepossible by the gear unit. A further advantage in such a construction ofthe gear unit consists in the high efficiencies which can be realized.

“Operative connection” or “driving connection” means a connectionbetween two torque-conducting parts which allows a torque or power to betransferred between these parts. In particular, the two parts arecorrespondingly rotatably mounted. Driving connections are connectionswhich have no gear ratio or intermediate component parts but also thosehaving a gear ratio or intermediate component parts. For example, twoshafts or two toothed wheels can have further shafts and/or toothedwheels drivingly arranged therebetween.

The first planet carrier is connected to the electric machine at leastindirectly, in particular directly, i.e., fixed to rotate with a rotoror a rotor shaft of the electric machine. In rotor operation of theelectric machine, the rotor shaft of the electric machine serves asoutput shaft of the electric machine. The first ring gear is an inputshaft of the stepped planetary gearset in rotor operation of theelectric machine. In rotor operation of the electric machine, electricalenergy is fed to the electric machine from an energy accumulator, forexample, in particular a battery, as a result of which a rotation of therotor is brought about for generating a motive power. This motive poweris provided for driving the first planet carrier of the steppedplanetary gearset in rotation. Conversely, in generator operation,electrical energy is generated by the electric machine. The output shaftof the gear unit functions as input shaft of the gear unit in generatoroperation of the electric machine, whereas the first ring gear isaccordingly formed as output shaft of the gear unit, and a motive powerof the vehicle is conducted via the gear unit and the respective gearshifting element into the electric machine so that electrical energy isgenerated by the electric machine and can be fed into a battery forstorage. In generator operation, the output, for example, from one ormore rotating wheels of the vehicle is conducted into the electricmachine via the gear unit.

The expression “at least indirectly” means that two component parts areconnected to one another via at least one further component partarranged therebetween or are directly and, therefore, immediatelyconnected to one another. Consequently, still further component partscan be arranged between shafts or toothed wheels and operativelyconnected to the shaft or toothed wheel, respectively.

By “shaft”, be this an input shaft, an output shaft, an intermediateshaft or the like, is understood within the meaning of the invention arotatable component part of the powertrain for transmitting torques andvia which associated components of the powertrain are connected to oneanother so as to co-rotate or via which such a connection is producedwhen a corresponding shifting element or gear shifting element isactuated.

The first ring gear is in meshing engagement with a first toothed wheelof the respective stepped planet gear of the stepped planetary gearset,the first toothed wheel being arranged coaxial to and so as to co-rotatewith a second toothed wheel which, in turn, is in meshing engagementwith the second ring gear. The two toothed wheels of the respectivestepped planet gear have different diameters and/or different numbers ofteeth, the respective stepped planet gear being rotatably mounted at thefirst planet carrier jointly with the two toothed wheels. The advantagein providing a stepped planetary gearset consists in that a sun gear, inparticular two sun gears, of the stepped planetary gearset, can bedispensed with so that a cost-optimized gear unit is provided. Toothedwheels which engage with one another or mesh with one another transmit arotational speed and torque via their teeth which mesh with one another.

The first ring gear is operatively connected to the first gear shiftingelement and, when the first gear shifting element is shifted from theopen state into the closed state, is fastened relative to the housing orconnected to the housing so as to be fixed with respect to rotationrelative to it. The second gear shifting element, on the other hand, isconfigured to produce a direct drive of the stepped planetary gearset,which means that the motive power is transmitted directly, i.e., withoutconversion, to the output of the gear unit.

Depending on the shifting position or state of the two gear shiftingelements, the second ring gear transmits a motive power with arespective gear ratio at least indirectly to driven shafts of thevehicle which are at least indirectly connected, respectively, to atleast one wheel of the vehicle. The driven shafts are arranged coaxialto the output axis. Therefore, at least one wheel of the vehicle is atleast indirectly driven in rotation via the driven shaft by the motivepower generated with the electric machine and converted at least withthe gear unit.

By “gear shifting element” is meant a connection part by which at leastone torque-transmitting part is drivingly connectible to a furthertorque-transmitting part or to a stationary or fixed part. Therespective gear shifting element is shiftable between at least one openstate and a closed state. In the open state, the respective gearshifting element cannot transmit any torque between two partscooperating with the gear shifting element. In the closed state, therespective gear shifting element transmits a torque between the twoparts cooperating with the respective gear shifting element. Insofar asa driving connection exists between two gear unit elements, torques andforces and—depending on the construction of the gear unitelements—possibly a rotational speed are transmitted from a gear unitelement to the other gear unit element. The respective gear shiftingelement is formed to be positively engaging or frictionally engaging,for example.

When the first gear shifting element is in the closed state or isshifted into the closed state and the second gear shifting element isopen, a motive power is transmitted from the gear unit input to the gearunit output, or vice versa, in a first gear or a first gear step,namely, with a first gear ratio or a first transmission ratio. The firstring gear of the gear unit is supported against the housing or connectedto the housing so as to be fixed with respect to rotation relative toit. In the closed state of the first gear shifting element, the secondgear shifting element is in the open state so that a motive power istransmitted to the output shaft via the second ring gear of the gearunit. For example, a first gear ratio is greater than 1.

When the second gear shifting element is in the closed state, or isshifted into the closed state, and the first gear shifting element isopen, a motive power is transmitted from the gear unit input to the gearunit output, or vice versa, in a second gear or second gear step. Afirst element of the stepped planetary gearset is arranged to co-rotatewith a second element of the stepped planetary gearset, specifically insuch a way that the stepped planetary gearset is brought into a directdrive, and the motive power is transmitted with a second gear ratio orsecond transmission ratio. In direct drive, no conversion of the motivepower takes place so that the second transmission ratio in second gearor in the second gear step is i=1. It is advantageous in this respectthat an efficiency of nearly 100% is achieved when the stepped planetarygearset is in direct drive. The first transmission ratio differs fromthe second transmission ratio in order to realize two different gearsteps. Consequently, either the first gear shifting element or thesecond gear shifting element is closed in order to drive the vehicle.

According to an embodiment example of the invention, the second gearshifting element is arranged in the gear unit in a first locking variantof the stepped planetary gearset in such a way that when the second gearshifting element is closed a rotationally fixed connection orinterlocking between the first ring gear and first planet carrier isbrought about. In this case, the first ring gear is the first element ofthe stepped planetary gearset and the first planet carrier is the secondelement of the stepped planetary gearset. When the second gear shiftingelement is closed, these two elements are fixed to rotate with oneanother in order to realize the direct drive of the stepped planetarygearset.

According to a second locking variant of the stepped planetary gearset,the second gear shifting element is arranged in the gear unit such thatwhen the second gear shifting element is closed a rotationally fixedconnection or interlocking between the first ring gear and the secondring gear is brought about. In this case, the first ring gear is thefirst element of the stepped planetary gearset and the second ring gearis the second element of the stepped planetary gearset and, when thesecond gear shifting element is closed, these two elements are fixed torotate with one another in order to realize the direct drive of thestepped planetary gearset.

According to a third locking variant of the stepped planetary gearset,the second gear shifting element is arranged in the gear unit such thatwhen the second gear shifting element is closed a rotationally fixedconnection or interlocking between the first planet carrier and thesecond ring gear is brought about. In this case, the first planetcarrier is the first element of the stepped planetary gearset and thesecond ring gear is the second element of the stepped planetary gearset.When the second gear shifting element is closed, these two elements areconnected to one another so as to be fixed with respect to rotationrelative to one another in order to realize the direct drive of thestepped planetary gearset.

In the closed state of the second gear shifting element, the first gearshifting element is in the open state so that the motive power istransmitted to the output shaft via the second ring gear. Consequently,either the first gear shifting element or the second gear shiftingelement is in the closed state for rotationally driving the output shaftof the gear unit.

If both gear shifting elements are open, no motive power is introducedinto the gear unit and, accordingly, no motive power is transmitted tothe output shaft of the gear unit. Thus the gear unit is idling. On theother hand, if both gear shifting elements are closed, a rotation of theoutput shaft is blocked. To this extent, the two gear shifting elementsare simultaneously in a closed state in order to realize a park lockfunction.

The first gear shifting element and/or the second gear shifting elementis preferably formed as a frictionally engaging shifting element. Inparticular, the frictionally engaging shifting element can be formed asa friction-type shifting element, especially as a multiple-disk clutchor cone clutch, in order to produce a frictionally engaging connectionbetween the first ring gear and the housing and/or between the furtherelements of the gear unit which are to be coupled in order to realizethe direct drive described above. A frictionally engaging shiftingelement is one that introduces a normal force to two parts or surfacesof gear unit elements to be connected to one another, a mutualdisplacement of the parts or surfaces being prevented until acounterforce brought about substantially by static friction is exceeded.Accordingly, a frictional engagement is formed for transferring a torquebetween the respective gear unit elements to be connected.

According to the first aspect of the invention, a power shifting betweenthe gears or the two gear steps, that is, a shifting between a firstgear and a second gear, or vice versa, is advantageously possible withthe gear unit according to the invention without interrupting the motivepower at the output or at the output shaft particularly during ashifting process. It is advantageous that separate power shiftingelements need not be provided for this purpose. Rather, the gear unitcan be outfitted with frictionally engaging gear shifting elementshaving a simpler construction. For traction shifting or coastingshifting, it is required that at least one of the gear shifting elementsis constructed as a frictionally engaging gear shifting element or as afriction-type shifting element. However, for traction shifting andcoasting shifting by the gear shifting elements, it is required thatboth gear shifting elements are constructed as frictionally engaginggear shifting elements. On the other hand, the other respective gearshifting element not formed as frictionally engaging shifting elementcan be formed as positively engaging gear shifting element or jaw-typeshifting element. Accordingly, a gear shifting element or both gearshifting elements can realize a power shift. A gear shifting elementwhich realizes a power shift is a shifting element that allows two gearunit elements to be connected to one another, while a motive power,particularly a torque, is applied to the one gear unit element so thatthe motive power is transmitted to the other respective gear unitelement after closing. It is not necessary to synchronize the speeds ofthe gear unit elements in question before a power shifting element isclosed.

Alternatively, the first gear shifting element and/or the second gearshifting element is formed as a positively engaging shifting element. Apositively engaging shifting element can be formed, for example, as ajaw-type shifting element for realizing a positively engaging connectionbetween the first ring gear and the housing and/or between the furtherelements of the gear unit which are to be coupled for realizing thedirect drive. A positively engaging shifting element is one in which twoparts of the gear unit engage one inside the other and form a positiveengagement for transmitting a torque between two gear unit elements.Compared to the frictionally engaging shifting element, a positivelyengaging shifting element is cheaper and, above all,efficiency-optimized.

According to an embodiment form of the invention, the two gear shiftingelements are formed jointly as a double shifting element. This meansthat the first gear shifting element and second gear shifting elementare arranged directly axially adjacent one another and the two gearshifting elements are combined to form a unit. This is particularlyadvantageous when both shifting elements are constructed as jaw-typeshifting elements for realizing a positively engaging connection. Inthis case, no power shifting is possible between first gear and secondgear, or vice versa, but axial installation space for the gear unit canbe saved by arranging and configuring the gear shifting elements in thisway. Moreover, the construction of the gear shifting elements asjaw-type shifting elements facilitates realization of the park lockfunction, i.e., when the two gear shifting elements are moved into, orare in, the closed state.

According to a second aspect of the invention, a powertrain for an atleast partially electrically driven vehicle comprises a gear unitaccording to the first aspect of the invention, an electric machine anda differential which drivingly connects the gear unit to two drivenshafts arranged coaxial to an output axis. A powertrain of this kind iscompactly constructed with the gear unit according to the invention andrealizes a comparatively high ratio step.

The differential is preferably formed as bevel gear differential.Further, other alternative embodiment forms of the differential are alsoconceivable, for example, a spur gear differential or planetarydifferential. The motive power coming from the gear unit with a firstgear ratio or second gear ratio is transmitted from the output shaft ofthe gear unit to the two driven shafts at least indirectly via thedifferential. The differential distributes the motive power, i.e., arotational speed and a torque, to the driven shafts. The differential isalso arranged on the output axis so that the driven shafts extendcoaxial to the output axis. A differential formed as bevel geardifferential has two output elements on the wheel side, particularly afirst driven wheel and a second driven wheel. The two driven wheelsmesh, respectively, with a compensating element. The compensatingelements are mounted in a differential carrier so as to be rotatablearound their own axes. The respective driven wheel is connected to therespective driven shaft so as to be fixed with respect to rotationrelative to it. The differential is driven via the differential carrier.

The powertrain preferably comprises a planetary gear assembly which isdrivingly connected to the output shaft of the gear unit and has atleast a first planetary gearset. The first planetary gearset isadvantageously formed, i.e., configured as a negative planetary gearset,and an overall gear ratio is increased by the respective planetarygearset of the planetary gear assembly depending on the respective gearspeed selected in the gear unit. An overall gear ratio between 6 and13.5 is preferably realizable by the planetary gear assembly arranged inthe power flow downstream of the gear unit. A negative planetary gearsetis formed of a sun gear, planet carrier and ring gear. The planetcarrier guides at least one, but preferably a plurality of rotatablymounted planet gears, each of which meshes or is in meshing engagementwith the sun gear as well as with the surrounding ring gear.

In particular, the first planetary gear set of the planetary gearassembly has a first sun gear, a third ring gear which is fixed withrespect to the housing and a plurality of planet gears rotatably mountedon a second planet carrier, the first sun gear being connected to thesecond ring gear of the gear unit so as to be fixed with respect torotation relative to it. The planetary gear assembly is formed to beaxially compact, the planet gears being in meshing engagement with thethird ring gear as well as with the first sun gear. Further, the secondplanet carrier rotatably receiving the planet gears is operativelyconnected to a second output shaft which can advantageously be guidedaxially through the gear unit and/or the electric machine in order toconduct the motive power into the differential and save axialinstallation space at the same time.

A differential carrier of the differential is preferably connected tothe second planet carrier of the planetary gear assembly so as to befixed with respect to rotation relative to it. Further, it isconceivable that the second output shaft is formed on the inner side tobe at least partially hollow so that one of the two driven shafts of thedifferential can be guided through axially. In other words, the secondoutput shaft can be arranged radially inside of the first planet carrierof the gear unit, and one of the two driven shafts of the differentialcan be arranged radially inside of the second output shaft.

At least the gear unit and/or the differential are/is preferablyarranged at least partially or completely spatially inside of the rotorof the electric machine. Arranging the gear unit and/or the differentialradially inside of the rotor can save axial installation space of thepowertrain. Consequently, the powertrain is formed axially compact. Forexample, the gear unit is arranged completely spatially inside of therotor of the electric machine. The differential is arranged completelyspatially inside of the rotor of the electric machine, for example.

According to an embodiment example of the invention, at least a firsttransmission stage is drivingly arranged between the output shaft of thegear unit and the differential. In particular, the output shaft of thegear unit is arranged paraxial to the output axis. Accordingly, theoutput axis on which the driven shafts of the powertrain are arranged isparaxial to an input axis. At least the output shaft of the gear unit,preferably also the input shaft of the gear unit and/or the rotationalaxis of the rotor of the electric machine are arranged coaxial to theinput axis.

The first transmission stage is advantageously formed to increase theoverall gear ratio and preferably comprises at least two tooth wheels inmeshing engagement with one another, the rotational axis of the firsttoothed wheel being arranged coaxial to the output shaft of the gearunit, and the rotational axis of a further toothed wheel being arrangedcoaxial to the output axis. The first transmission stage can comprise aspur gear stage, for example.

Additionally, a second transmission stage can be provided, and themotive power is introduced at least indirectly into the differentialfrom the gear unit via the first transmission stage and the secondtransmission stage. An intermediate shaft is provided which is arrangedparallel to the output shaft of the gear unit and to the output axis ofthe vehicle. Two further toothed wheels are preferably arranged on theintermediate shaft. The first toothed wheel of the intermediate shaftmeshingly engages with a toothed wheel which is operatively connected atleast indirectly to the output shaft, and the second toothed wheel ofthe intermediate shaft meshingly engages with a further toothed wheel atleast indirectly operatively connected to the differential. The twotransmission stages are formed as spur gear stages, for example, and canincrease the overall gear ratio, the gear ratio being carried out in twostages. As a result of the axial offset, axial installation space of thepowertrain is saved particularly along the input axis.

As an alternative to the bevel gear differential, the differential canbe formed as an integral differential, as it is called, which has asecond planetary gearset and a third planetary gearset, each planetarygearset being drivingly connected to a respective driven shaft. A firstoutput torque is transmittable to the first driven shaft by the secondplanetary gearset, and a supporting torque of the second planetarygearset can be converted in the third planetary gearset in such a waythat a second output torque corresponding to the first output torque istransmittable to the second driven shaft.

By an “integral differential” is meant a differential with two planetarygearsets in which the second planetary gearset is drivingly connected toan input shaft of the differential and also to the third planetarygearset. The input shaft of the differential is at least indirectlyconnected to the output shaft of the gear unit. Alternatively, the inputshaft of the differential can be connected integral to the output shaftof the gear unit. The second planetary gearset is drivingly connected tothe first driven shaft. The third planetary gearset is drivinglyconnected to the second driven shaft. Further, the third planetarygearset is at least indirectly supported at a stationary housing of thegear unit or at the chassis of the motor vehicle, that is, connectedthereto so as to be fixed with respect to relative rotation.

By an integral differential, the input torque of the input shaft of thedifferential is convertible and can be divided and transmitted to thetwo driven shafts in a defined ratio. The input torque is preferablytransmitted at fifty percent, respectively, i.e., halved, to the drivenshafts. Accordingly, the differential has no component part to which thesum of the two output torques is applied. Beyond this, with the speedsof the driven shafts being identical, the differential has no gear teethrevolving as a block or revolving without rolling motion. In otherwords, there is always a relative movement of the component parts of therespective planetary gearset which are in meshing engagement with oneanother irrespective of the output speeds of the driven shafts. Thedifferential performs the function of generating the overall gear ratioand functions as a differential at the same time. In other words, theintegral differential realizes a torque increase and an apportioning ofmotive power. Further, there is also a reduction in weight.

The integral differential and the driven shafts are preferably adaptedto be arranged coaxial to the output axis of the vehicle. Accordingly,the output axis extends coaxial to the input axis, namely, inparticular, coaxial to the rotational axis of the rotor of the electricmachine, coaxial to the input shaft of the gear unit and/or coaxial tothe output shaft of the gear unit.

The powertrain according to the invention and the gear unit according tothe invention are useable in all-electric vehicles as well as in hybridvehicles which are drivable partially electrically and partially by aseparate internal combustion engine. Depending on the construction andquantity of driven axles, the vehicle can also comprise two or more suchpowertrains or gear units, respectively, and one axle, a plurality ofaxles or all axles of the vehicle can be outfitted with the respectivepowertrain according to the invention and can be constructed to bedrivable by means thereof. Such a vehicle is a motor vehicle,particularly a passenger car, utility vehicle or truck.

It shall be understood that features of the present solutions describedin the claims and/or drawings can also possibly be combined so that theachievable advantages and effects can be implemented cumulatively.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in the following with reference todrawings depicting the various embodiment forms of the invention. Likeor similar elements are designated with consistent reference numerals.In particular, the drawings show:

FIG. 1 a vehicle comprising a powertrain according to the invention witha gear unit according to the invention in a first embodiment form;

FIG. 2A a schematic depiction of the gear unit according to theinvention shown in FIG. 1 ;

FIG. 2B a schematic depiction of the gear unit according to theinvention in a second embodiment form;

FIG. 2C a schematic depiction of the gear unit according to theinvention in a third embodiment form;

FIG. 3 a schematic diagram of a shifting matrix relating to shiftingstates for driving with a gear unit according to the invention shown inFIG. 1 and FIG. 2A;

FIG. 4 a schematic depiction of the powertrain according to theinvention with the gear unit according to the invention shown in FIG. 1and FIG. 2A;

FIG. 5 a schematic depiction of the powertrain according to theinvention with the gear unit according to the invention in a fourthembodiment form;

FIG. 6 a schematic depiction of the powertrain according to theinvention with the gear unit according to the invention in a fifthembodiment form;

FIG. 7 a schematic depiction of the powertrain according to theinvention with the gear unit according to the invention in a sixthembodiment form; and

FIG. 8 a schematic depiction of the powertrain according to theinvention with the gear unit according to the invention in a seventhembodiment form.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

FIG. 1 shows an electrically driven vehicle 1 with a powertrain 2according to the invention in a first embodiment form. The powertrain 2comprises an electric machine 11 which generates power and introducesthis power into a gear unit 3. The gear unit 3 is shown in FIGS. 2A to2C, and the associated shifting matrix is shown in FIG. 3 . The gearunit 3 is drivingly connected to a planetary gear assembly 14 whichincreases an overall gear ratio and transmits the power to adifferential 16 which is arranged downstream in the power flow, in thisinstance spatially inside of the electric machine 11. The differential16 divides the motive power between a first driven shaft 18 a and asecond driven shaft 18 b which are in turn operatively connected to adriven wheel 28 of the vehicle 1 in each instance.

The vehicle 1 can further comprise an energy accumulator—not shown—whichis supplied with electrical energy by the electric machine 11 ingenerator mode when the power flow is reversed. The energy accumulatorcan be a battery or the like, for example. Accordingly, in generatormode, by the electric machine 11, electrical energy is generated, storedand conserved for resupplying the electric machine 11.

The gear unit 3 from FIG. 1 is shown in a detailed diagram in FIG. 2A.The gear unit 3 according to FIGS. 2A to 2C can be acted upon by amotive power in the powertrain 2 according to FIG. 4 via an input shaft29 with a rotor 19 of the electric machine 11, which rotor 19 is mountedso as to be rotatable relative to a stator 30. The input shaft 29 can beconnected to the rotor 19 integrally or in more than one part; in anycase, a rotationally locked driving connection exists.

The gear unit 3 comprises a stepped planetary gearset 4 with a firstring gear 8 a, a second ring gear 8 b and a plurality of stepped planetgears 10 rotatably mounted at a first planet carrier 9, the first planetcarrier 9 being connected to the input shaft 29 so as to be fixed withrespect to rotation relative to it. The gear unit 3 further has a firstgear shifting element 5 and a second gear shifting element 6. The firstgear shifting element 5 is adapted to connect the first ring gear 8 a toa housing 13 so as to be fixed with respect to rotation relative to itin a closed state, and the second gear shifting element 6 is adapted toimplement a direct drive of the stepped planetary gearset 4. To drivethe output shaft 12 in rotation, one of the two gear shifting elements5, 6 is in the closed state.

Accordingly, the driving of the gear unit 3 is carried out via the firstplanet carrier 9. The output is carried out via the second ring gear 8 bwhich is connected to an output shaft 12 of the gear unit 3 so as to befixed with respect to rotation relative to it and is in meshingengagement with a second toothed wheel 31 b of the respective steppedplanet gear 10. In addition to the second toothed wheel 31 b, eachstepped planet gear 10 also has a first toothed wheel 31 a which isaxially adjacent the second toothed wheel 31 b and connected thereto soas to be fixed with respect to rotation relative to it and which is inmeshing engagement with the first ring gear 8 a. Accordingly, therespective stepped planet gear 10 can be arranged as shaft with twotoothed wheels 31 a, 31 b arranged thereon so as to be fixed withrespect to rotation relative to it. The two toothed wheels 31 a, 31 bare arranged axially spaced at the respective stepped planet gear 10 andhave different diameters and numbers of teeth. In the present case, thefirst toothed wheel 31 a of the respective stepped planet gear 10 has agreater diameter than the second toothed wheel 31 b of the respectivestepped planet gear 10.

When the first gear shifting element 5 is in a closed state or isshifted into the closed state and the second gear shifting element 6 isin an open state, the first ring gear 8 a is connected against thehousing 13 so as to be fixed with respect to rotation relative to it sothat a motive power of the electric machine 11 is conducted via thefirst planet carrier 9 to the stepped planet gears 10 and then via thesecond ring gear 8 b to an output shaft 12 of the gear unit 3. When thesecond gear shifting element 6 is moved or shifted into the closed stateand the first gear shifting element 5 is in the open state, the firstring gear 8 a is connected against the first planet carrier 9 so as tobe fixed with respect to rotation relative to it so that the steppedplanetary gearset 4 is moved into a direct drive. In direct drive, thereis no conversion of torques and/or rotational speeds, a second gearratio of i=1 is realized, and the output shaft 12 is driven via thesecond ring gear 8 b corresponding to the second gear ratio. As a resultof the first ring gear 8 a being connected via the second gear shiftingelement 6 to the first planet carrier 9 so as to be fixed with respectto rotation relative to it, the direct drive is produced withcomparatively small supporting torques.

In an open state of the respective gear shifting element 5, 6, no torqueis transmitted via the respective gear shifting element 5, 6, whereas ina closed state of the respective gear shifting element 5, 6, a torque istransmitted via the respective gear shifting element 5, 6.

FIG. 3 shows a shifting matrix for a first gear step E1 and a secondgear step E2 of the gear unit 3. The respective gear shifting element 5,6 is closed where indicated by the “X” and open where there is no “X”.An electric forward drive of the vehicle 1 with respective gear ratio isrealized via the respective gear step E1, E2. When the first gearshifting element 5 is closed and the second gear shifting element 6 isopen, the first gear step E1 is engaged and a first gear ratio isaccordingly realized. When the second gear shifting element 6 is closedand the first gear shifting element 5 is open, the second gear step E2is engaged and a second gear ratio which is not equal to the first gearratio is accordingly realized. This shifting matrix applies to all ofthe depicted embodiment examples of the invention. Traction powershifting and/or coasting power shifting may be realized depending on theconstruction of the gear shifting elements 5, 6. In such a case, therespective gear shifting element 5, 6 is formed as a powershift element.

According to FIG. 2A, the first gear shifting element 5 is formed as apositively engaging shifting element, in this case as a jaw-typeshifting element. In the closed state of the first gear shifting element5, a positively engaging connection is accordingly produced between thefirst ring gear 8 a and the housing 13. Ideally, these parts aresynchronized before entering the positively engaging connection. On theother hand, the second gear shifting element 6 is formed in the presentcase as frictionally engaging shifting element, in this instance as adisk-type shifting element. In the closed state of the second gearshifting element 6, a frictionally engaging connection is producedbetween the first planet carrier 9 and the first ring gear 8 a torealize the direct drive of the stepped planetary gearset 4. Asynchronization of the rotational speeds of the parts is not required,and a frictionally engaging shifting element is suitable as powershifting element. In other words, the second gear shifting element 6realizes a traction power shifting from gear step E1 into gear step E2,or vice versa. The load during shifting processes between gear steps E1,E2 is supportable by the first gear shifting element 5 configured aspositively engaging until the second gear shifting element 6 iscompletely open or closed to prevent a load decrease at the outputparticularly during shifting processes.

FIG. 2B shows a second alternative embodiment form of the gear unit 3with a second locking variant in contrast to the embodiment exampleaccording to FIG. 2A. The gear unit 3 comprises a stepped planetarygearset 4 with a first ring gear 8 a, a second ring gear 8 b and aplurality of stepped planet gears 10 rotatably mounted at a first planetcarrier 9, the planet carrier 9 being connected to the input shaft 29 soas to be fixed with respect to rotation relative to it. Therefore, thedrive is carried out via the first planet carrier 9. The output iscarried out via the second ring gear 8 b which is connected to an outputshaft 12 of the gear unit 3 so as to be fixed with respect to rotationrelative to it and which is in meshing engagement with a second toothedwheel 31 b of the respective stepped planet gear 10. In addition to thesecond toothed wheel 31 b, each stepped planet gear 10 also has a firsttoothed wheel 31 a which is axially adjacent and connected thereto so asto be fixed with respect to relative rotation and which is in meshingengagement with the first ring gear 8 a. In the present case, the firstring gear 8 a is operatively connected to a first gear shifting element5 via which the first ring gear 8 a is connectible to a housing 13 so asto be fixed with respect to rotation relative to it. The steppedplanetary gearset 4 can be shifted into direct drive by the second gearshifting element 6. In the present case, the first ring gear 8 a isconnectible to the second ring gear 8 b so as to co-rotate therewith byshifting the second gear shifting element 6 into the closed state, andthe above-described direct drive of the stepped planetary gearset 4 isaccordingly realized in second gear. In other words, the second gearshifting element 6 is formed to produce a fixed rotational connectionbetween the first ring gear 8 a and the second ring gear 8 b. The secondgear shifting element 6 is arranged in the present instance axiallybetween the stepped planetary gearset 4 of the gear unit 3 and the firstgear shifting element 5. In other respects, the gear unit 3 describedhere functions analogous to the gear unit 3 according to FIG. 2A.

A third alternative embodiment of the gear unit 3 with a third lockingvariant is shown in FIG. 2C. The gear unit 3 comprises a steppedplanetary gearset 4 with a first ring gear 8 a, a second ring gear 8 band a plurality of stepped planet gears 10 rotatably mounted at a firstplanet carrier 9, the planet carrier 9 being connected to the inputshaft 29 so as to be fixed with respect to rotation relative to it.Therefore, driving is carried out via the first planet carrier 9. Theoutput is carried out via the second ring gear 8 b which is connected toan output shaft 12 of the gear unit 3 so as to be fixed with respect torotation relative to it and which is in meshing engagement with a secondtoothed wheel 31 b of the respective stepped planet gear 10. In additionto the second toothed wheel 31 b, each stepped planet gear 10 also has afirst toothed wheel 31 a which is axially adjacent and connected theretoso as to be fixed with respect to relative rotation and which is inmeshing engagement with the first ring gear 8 a. In the present case,the first ring gear 8 a is operatively connected to a first gearshifting element 5 via which the first ring gear 8 a is connectible to ahousing 13 so as to be fixed with respect to rotation relative to it.The stepped planetary gearset 4 can be shifted into direct drive by thesecond gear shifting element 6. The direct driving of the steppedplanetary gearset 4 is realized in that a rotationally fixed connectionis produced between the second ring gear 8 b and the first planetcarrier 9 by shifting the second gear shifting element 6 into the closedstate so that the above-described direct drive is accordingly realizedin second gear. In other words, the second gear shifting element 6 isformed to produce a fixed rotational connection between the second ringgear 8 b and the first planet carrier 9. The second gear shiftingelement 6 is likewise arranged in the present instance axially betweenthe stepped planetary gearset 4 and the first gear shifting element 5.In other respects, the gear unit 3 described here functions analogous tothe gear unit 3 according to FIG. 2A.

FIG. 4 shows the powertrain 2 which has the gear unit 3 described inFIG. 2A. In this respect, reference is made to the statements referringto FIG. 1 , FIG. 2A and FIG. 3 . FIG. 4 also shows the electric machine11 which is connected via the input shaft 29 to the first planet carrier9 so as to be fixed with respect to rotation relative to it.Alternatively, the two gear shifting elements 5, 6 may be configured asin the respective embodiment form according to FIG. 5 , FIG. 6 or FIG. 7. Further, the powertrain 2 has a planetary gear assembly 14 with afirst planetary gearset 15. In the present case, the gear unit 3 isarranged axially between the planetary gear assembly 14 and the electricmachine 11. In the present case, the first planetary gearset 15 isconfigured as a negative planetary gearset and comprises a first sungear 20 connected to the output shaft 12 of the gear unit 3 so as to befixed with respect to rotation relative to it, a stationary third ringgear 21 which is connected to the housing 13 so as to be fixed withrespect to rotation relative to it, and a plurality of planet gears 23rotatably mounted at a second planet carrier 22. The first sun gear 20is drivingly connected to the second ring gear 8 b of the gear unit 3via output shaft 12 such that the planetary gear assembly 14 issubsequently operatively connected to the output shaft 12 on the driveside. The output of the planetary gear assembly 14 is carried out viathe second planet carrier 22 which is drivingly connected to adifferential 16. Total gear ratios between 6 and 13.5, for example, canbe realized by such a combination comprising gear unit 3 and planetarygear assembly 14.

In the present case, the differential 16 is configured as a bevel geardifferential and drivingly connects the gear unit 3 via the planetarygear assembly 14 to the two driven shafts 18 a, 18 b arranged coaxial toan output axis 17, the second driven shaft 18 b being guided through thegear unit 3 and the planetary gear assembly 14 in the present instance.The bevel gear differential 16 known from the prior art has two outputelements on the wheel side which are configured as a first driven wheel16 b and second driven wheel 16 c. The driven wheels 16 b, 16 c mesh,respectively, with a compensating element 16 d, 16 e. The compensatingelements 16 d, 16 e are mounted in a differential carrier 16 a so as tobe rotatable around their own axes. The first driven wheel 16 b isconnected to the first driven shaft 18 a so as to be fixed with respectto rotation relative to it, and the second driven wheel 16 c isconnected to the second driven shaft 18 b so as to be fixed with respectto rotation relative to it. The differential carrier 16 a of thedifferential 16 is connected via an intermediate shaft 32 to the secondplanet carrier 22 so as to be fixed with respect to rotation relative toit, the intermediate shaft 32 being guided through the gear unit 3coaxial to the input shaft 29 and output shaft 12 of the gear unit 3 andconnected to the differential carrier 16 a. The differential 16 isarranged completely spatially inside of the rotor 19 of the electricmachine 11 in order to save axial installation space. Accordingly, inthis case the output axis 17 extends coaxial to an input axis 33, andthe rotational axis of the rotor 19, the input shaft 29 and the outputshaft 12 of the gear unit 3 are arranged coaxial to the input axis 33.Consequently, the gear unit 3 is arranged axially between the electricmachine 11 and the differential 16 on one side and the planetary gearassembly 14 on the other side.

The powertrain according to FIG. 5 comprises the gear unit 3 from FIG.2B with the difference that the two gear shifting elements 5, 6 areconfigured as jaw-type shifting elements and are combined to form adouble shifting element 40. Therefore, reference is made to thestatements relating to the gear unit 3 from FIG. 2B. Alternatively, thetwo gear shifting elements 5, 6 may be configured as in the respectiveembodiment form according to FIG. 4 , FIG. 6 or FIG. 7 . Further, it isconceivable to form the gear unit 3 as in the respective embodimentexample according to FIG. 2A or FIG. 2C. Reference is made to thedescription relating to FIG. 3 for the shifting between the first gearstep E1 and second gear step E2. The gear unit 3 comprising the steppedplanetary gearset 4 and the two gear shifting elements 5, 6 is arrangedspatially completely inside of the rotor 19 of the electric machine 11in order to save axial installation space and make the powertrain 2 morecompact. The gear shifting elements 5, 6 are arranged directly adjacentone another coaxial to the input axis 33 and output axis 17 and togetherform the double shifting element 40 which is compactly comprised of thetwo gear shifting elements 5, 6. The first gear shifting element 5realizes a positively engaging connection between housing 13 and firstring gear 8 a in the closed state. The second gear shifting element 6realizes a positively engaging connection between the first ring gear 8a and the second ring gear 8 b in the closed state. A particularlycost-optimized and efficiency-optimized clutch system is provided inthis way.

The first planetary gearset 15 of the planetary gear assembly 14 isconfigured as a negative planetary gearset and comprises a first sungear 20 connected to the output shaft 12 of the gear unit 3 so as to befixed with respect to rotation relative to it, a stationary third ringgear 21 connected to the housing 13 so as to be fixed with respect torotation relative to it, and a plurality of planet gears 23 rotatablymounted at a second planet carrier 22. The first sun gear 20 isconnected to the second ring gear 8 b of the gear unit 3 via outputshaft 12 so as to be fixed with respect to rotation relative to it suchthat the planetary gear assembly 14 is subsequently operativelyconnected to the output shaft 12 on the drive side. The output of theplanetary gear assembly 14 is carried out via the second planet carrier22 which is connected to a differential carrier 16 a of the differential16 so as to be fixed with respect to rotation relative to it. Thedifferential 16 is configured as a bevel gear differential and isfurther identical to the differential 16 according to FIG. 4 so that therelevant statements apply here. Total gear ratios of between 6 and 13.5,for example, can be achieved by such a combination comprising gear unit3 and planetary gear assembly 14.

The differential 16 drivingly connects the gear unit 3 to the drivenshafts 18 a, 18 b via the planetary gear assembly 14. In the presentcase, the first driven shaft 18 a is guided axially through the gearunit 3 and the electric machine 11. The planetary gear assembly 14 isarranged axially between the electric machine 11 and the gear unit 3 onthe one hand and the differential 16 on the other hand. Alternatively,it is conceivable that the differential 16 is also arranged togetherwith the gear unit 3 spatially inside of the rotor 19 of the electricmachine 11 in order to save additional axial installation space. Thedifferential 16 is drivingly connected to the second planet carrier 22via an intermediate shaft 32. The intermediate shaft 32 is arrangedcoaxial to the output shaft 12 of the gear unit 3. In this instance, theoutput axis 17 is also arranged coaxial to an input axis 33.

The powertrain 2 according to FIG. 6 comprises the gear unit 3 from FIG.2A with the difference that the two gear shifting elements 5, 6 areconfigured as jaw-type shifting elements. Therefore, reference is madeto the statements pertaining to the gear unit 3 from FIG. 2A. Further,it is conceivable to form the gear unit 3 as in the respectiveembodiment example according to FIG. 2B or FIG. 2C. Reference is made tothe description of FIG. 3 for the shifting between the first gear stepE1 and the second gear step E2. FIG. 6 shows a third embodiment exampleof the powertrain 2 according to the invention. In the present instance,the gear unit 3 comprising the stepped planetary gearset 4 and the twogear shifting elements 5, 6 are arranged spatially completely inside ofthe rotor 19 of the electric machine 11 in order to save axialinstallation space of the powertrain 2. The first gear shifting element5 realizes a positively engaging connection between the housing 13 andthe first ring gear 8 a in the closed state. The second gear shiftingelement 6 realizes a positively engaging connection between the firstring gear 8 a and the first planet carrier 9 in the closed state. Aparticularly cost-optimized and efficiency-optimized clutch system isprovided in this way. Alternatively, it is conceivable that therespective gear shifting elements 5, 6 formed in each instance asjaw-type shifting element are combined and configured as a doubleshifting element as in FIG. 5 . Further alternatively, the two gearshifting elements 5, 6 can be configured as in the respective embodimentform according to FIG. 4 or FIG. 7 .

In contrast to the powertrains 2 according to FIG. 4 and FIG. 5 whichhave a differential 16 configured as a bevel gear differential, thepowertrain 2 according to FIG. 6 comprises a differential 16 configuredas an integral differential 25 with a second planetary gearset 26 andthird planetary gearset 27. The two planetary gearsets 26, 27 arearranged either axially adjacent one another or radially one above theother depending on the requirements of the integral differential 25,particularly the gear ratio to be realized by the integral differential25. In the present case, the planetary gearsets 26, 27 are arrangedradially one above the other so that axial installation space of thepowertrain 2 is saved. In other words, the planetary gearsets 26, 27 liein a common plane perpendicular to the driven shafts 18 a, 18 b oroutput axis 17, respectively. Consequently, the integral differential 25is constructed in a radially nested type of construction.

A first output torque can be transmitted to the first driven shaft 18 aby the second planetary gearset 16. A supporting torque of the secondplanetary gearset 26 acting opposite the first output torque istransmitted to the third planetary gearset 27 and is convertible in thethird planetary gearset 27 in such a way that a second output torquecorresponding to the first output torque can be transmitted to thesecond driven shaft 18 b. Consequently, the integral differential 25 isconfigured as a planetary gear assembly. The integral differential 25 isoperatively connected to the gear unit 3 via the input shaft of theintegral differential 25 which is simultaneously the output shaft 12 ofthe gear unit 3. The output at the integral differential 25 is carriedout via the two driven shafts 18 a, 18 b. In other words, a motive poweris distributed to two driven shafts 18 a, 18 b by the integraldifferential 25. In the present case, the first driven shaft 18 aextends in direction of the gear unit 3 and electric machine 11 and isaxially guided through the gear unit 3 and the electric machine 11. Thesecond driven shaft 18 b extends away from the powertrain 2 in theopposite direction. Due to the fact that the integral differential 25which increases a torque coming from the gear unit 3 is only arranged atthe end of the powertrain 2, the component parts arranged upstreamthereof in the power flow can be formed comparatively small and slenderso that production is more economical and the overall weight of thepowertrain 2 is reduced. The driven shafts 18 a, 18 b, the integraldifferential 25, the electric machine 11 and the gear unit 3 arearranged coaxial to the input axis 33 of the gear unit 3 and to theoutput axis 17 of the vehicle 1.

The output shaft 12 of the gear unit 3 is connected to a second sun gear34 a of the second planetary gearset 26 so as to be fixed with respectto rotation relative to it. Accordingly, the second ring gear 8 b isconnected to the second sun gear 34 a so as to be fixed with respect torotation relative to it. The transmission of power from the secondplanetary gearset 26 to the third planetary gearset 27 is carried outvia a coupling shaft 35 which is connected to a fourth ring gear 36 a ofthe second planetary gearset 26 so as to be fixed with respect torotation relative to it on the one hand and, on the other hand, isconnected to a third sun gear 34 b of the third planetary gearset 27 soas to be fixed with respect to rotation relative to it. Consequently,the coupling shaft 35, the fourth ring gear 36 a and the third sun gear34 b are connected integral with one another. The coupling shaft 35 withthe fourth ring gear 36 a and the third sun gear 34 b can also beconfigured as a ring gear which has not only an inner toothing but alsoan outer toothing. A plurality of second planetary gears 37 a isarranged spatially between the second sun gear 34 a and the fourth ringgear 36 a, in the present instance so as to be rotatable on a rotatablymounted third planet carrier 38 a. Further, a plurality of thirdplanetary gears 37 b which are arranged in the present case so as to berotatable on a fourth planet carrier 38 b fixed with respect to thehousing are arranged on the same radially extending plane and radiallyoutside of the second planetary gearset 26 spatially between the thirdsun gear 34 b and a fifth ring gear 36 b of the third planetary gearset27. The first output on the first driven shaft 18 a is carried out viathe third planet carrier 38 a of the second planetary gearset 26, whichthird planet carrier 38 a is connected to the first driven shaft 18 a soas to be fixed with respect to rotation relative to it. The secondoutput on the second driven shaft 18 b is carried out via the fifth ringgear 36 b of the third planetary gearset 27, which fifth ring gear 36 bis connected to the second driven shaft 18 b so as to be fixed withrespect to rotation relative to it.

According to a sixth alternative embodiment example of the powertrain 2shown in FIG. 7 , the gear unit 3 is arranged axially between theelectric machine 11 and the differential 16, the differential 16 beingarranged on the output axis 17 which is arranged paraxial to the inputaxis 33 in the present case. Accordingly, the output shaft 12 and theinput shaft 29 of the gear unit 3 are also arranged on the input axis33. In the present case, the gear unit 3 is formed substantiallyidentical to the embodiment example according to FIG. 2A with respect toits functioning. The direct drive of the stepped planetary gearset 4 isrealized by shifting the second gear shifting element 6 into the closedstate with the attendant rotationally fixed connection between the firstring gear 8 a and the first planet carrier 9.

The output shaft 12 is drivingly connected via a transmission stage 24which, in the present case, is formed to be single-stage and whichcomprises a third toothed wheel 39 a which is connected to the outputshaft 12 so as to be fixed with respect to rotation relative to it and afourth toothed wheel 39 b which is operatively connected to thedifferential 16. In the present case, the toothed wheels 39 a, 39 b areconfigured as spur gears so that the transmission stage 24 consequentlycomprises a spur gear stage. The overall gear ratio of the powertrain 2is realized by the transmission stage 24 by suitably configured toothedwheel diameter and number of teeth. In this respect, an additionalplanetary gear assembly 14 corresponding to the embodiment examplesaccording to FIG. 4 and FIG. 5 can be dispensed with. However, dependingon the requirements of the powertrain, it may be useful to provide afurther gear unit for increasing a total gear ratio. As a result of theparaxial arrangement of the powertrain components, axial installationspace is economized in the powertrain 2, that is, in particular in thatthe electric machine 11 together with the gear unit 3 and thedifferential 16 are arranged at least partially adjacent one another. Inthis way, the electric machine 11 can also be made more slender, whichin turn has a positive effect on the axial spacing between the inputaxis 33 and output axis 17. In the present case, the differential 16 isconfigured as a bevel gear differential and, further, is identical tothe differential 16 according to FIG. 4 . Reference is made to therelevant statements.

In the present case, the gear shifting elements 5, 6 of the gear unit 3are formed in each instance as a disk-type shifting element and realizein each instance a frictionally engaging connection between the firstring gear 8 a and the housing 13 or between the first planetary carrier9 and the first ring gear 8 a, respectively, in the closed state. Inthis regard, it is advantageous that both traction shifts and coastingshifts can be power-shifted between the gear steps E1 and E2, or viceversa. In other words, the gear shifting elements 5, 6 are powershifting elements in the present case.

The load during shifting processes between the gear steps E1, E2 can besupported by the first gear shifting element 5 until the second gearshifting element 6 is completely open or closed, or vice versa, therebypreventing a load decrease at the output particularly during shiftingprocesses. Consequently, the powertrain 2 according to FIG. 7 comprisesthe gear unit from FIG. 2A with the difference that the two gearshifting elements 5, 6 are configured as disk-type shifting elements.Therefore, reference is made to the statements relating to the gear unit3 from FIG. 2A. Further, it is conceivable that the gear unit 3 isformed in the same manner as in the respective embodiment exampleaccording to FIG. 2B or FIG. 2C. As regards the shifting between thefirst gear step E1 and second gear step E2, reference is made to thedescription relating to FIG. 3 . Alternatively, the two gear shiftingelements 5, 6 can be configured as in the embodiment form according toFIG. 4 , FIG. 5 or FIG. 6 .

In a seventh alternative embodiment example according to FIG. 8 , thegear unit 3 is arranged axially between the electric machine 11 and thedifferential 16. Analogous to FIG. 7 , the differential 16 is arrangedon the output axis 17 paraxial to the input axis 33 on which the outputshaft 12 of the gear unit 3 lies. The output shaft 12 of the gear unit 3is operatively connected to the differential 16 via two transmissionstages 24, 7. The first transmission stage 24 comprises a third toothedwheel 39 a which is connected to the output shaft 12 so as to be fixedwith respect to rotation relative to it and a fourth toothed wheel 39 bwhich is connected to an intermediate shaft 32 arranged paraxial to theinput axis 33 and output axis 17 so as to be fixed with respect torotation relative to the intermediate shaft 32. Axially adjacent thefourth toothed wheel 39 b, a fifth toothed wheel 39 c of the secondtransmission stage 7 is arranged on the intermediate shaft 32 so as tobe fixed with respect to rotation relative to it, this intermediateshaft 32 being in meshing engagement with a sixth toothed wheel 39 doperatively connected to the differential 16. The overall gear ratio ofthe powertrain 2 is generated by the transmission stages 24, 7 bycorrespondingly configuring the toothed wheel diameters and number ofteeth of the toothed wheels 39 a-39 d. The toothed wheels 39 a-39 d areformed in the present instance as spur gears, and the transmissionstages 24, 7 are consequently spur gear stages. In this regard, anadditional planetary gear assembly 14 corresponding to the embodimentexamples according to FIG. 4 and FIG. 5 can be dispensed with. However,depending on the requirement for the powertrain 2, it may be useful toprovide a further gear unit for increasing a total gear ratio. Axialinstallation space is saved in the powertrain 2 through the paraxialarrangement of the powertrain components, particularly in that theelectric machine 11 together with the gear unit 3 and the differential16 are arranged at least partially adjacent one another. Accordingly,the electric machine 11 can be made more slender, which in turn has apositive effect on the axial spacing between the input axis 33 andoutput axis 17.

The two gear shifting elements 5, 6 of the gear unit 3 are arrangeddirectly adjacent one another coaxial to the input axis 33 and togetherform a double shifting element which combines the two gear shiftingelements 5, 6. In the present case, the gear shifting elements 5, 6 areeach configured as jaw-type shifting elements as in the embodimentexample according to FIG. 5 to which reference is made. It isconceivable that the gear unit 3 is configured as in the respectiveembodiment example according to FIG. 2B or FIG. 2C. For shifting betweenthe first gear step E1 and second gear step E2, reference is made to thedescription relating to FIG. 3 . Further, reference is made to thestatements relating to FIG. 7 and the reference numerals used therein,particularly to FIG. 2 and FIG. 5 . Alternatively, the two gear shiftingelements 5, 6 can be configured as in the respective embodiment formaccording to FIG. 4 , FIG. 6 or FIG. 7 . As a further alternative, thegear unit 3 can be arranged inside of the rotor 19 as in the embodimentforms according to FIG. 5 and FIG. 6 .

Thus, while there have shown and described and pointed out fundamentalnovel features of the invention as applied to a preferred embodimentthereof, it will be understood that various omissions and substitutionsand changes in the form and details of the devices illustrated, and intheir operation, may be made by those skilled in the art withoutdeparting from the spirit of the invention. For example, it is expresslyintended that all combinations of those elements and/or method stepswhich perform substantially the same function in substantially the sameway to achieve the same results are within the scope of the invention.Moreover, it should be recognized that structures and/or elements and/ormethod steps shown and/or described in connection with any disclosedform or embodiment of the invention may be incorporated in any otherdisclosed or described or suggested form or embodiment as a generalmatter of design choice. It is the intention, therefore, to be limitedonly as indicated by the scope of the claims appended hereto.

REFERENCE CHARACTERS

-   1 vehicle-   2 powertrain-   3 gear unit-   4 stepped planetary gearset-   5 first gear shifting element-   6 second gear shifting element-   7 second transmission stage-   8 a first ring gear-   8 b second ring gear-   9 first planet carrier-   10 stepped planet gears-   11 electric machine-   12 output shaft of the gear unit-   13 housing-   14 planetary gear assembly-   15 first planetary gearset-   16 differential-   16 a differential carrier-   16 b first driven wheel of the differential-   16 c second driven wheel of the differential-   16 d compensating element of the differential-   16 e compensating element of the differential-   17 output axis-   18 a first driven shaft-   18 b second driven shaft-   19 rotor of the electric machine-   20 first sun gear-   21 third ring gear-   22 second planet carrier-   23 first planet gear-   24 first transmission stage-   25 integral differential-   26 second planetary gearset-   27 third planetary gearset-   28 wheel of the vehicle-   29 input shaft of the gear unit-   30 stator of the electric machine-   31 a first toothed wheel of the stepped planetary gear-   31 b second toothed wheel of the stepped planetary gear-   32 intermediate shaft-   33 input axis-   34 a second sun gear of the integral differential-   34 b third sun gear of the integral differential-   35 coupling shaft of the integral differential-   36 a fourth ring gear-   36 b fifth ring gear-   37 a second planet gear-   37 b third planet gear-   38 a third planet carrier-   38 b fourth planet carrier-   39 a third toothed wheel of the transmission stage-   39 b fourth toothed wheel of the transmission stage-   39 c fifth toothed wheel of the transmission stage-   39 d sixth toothed wheel of the transmission stage-   40 double shifting element-   E1 first gear-   E2 second gear

1. A gear unit (3) for a powertrain (2) of an at least partially electrically driven vehicle (1), comprising: a stepped planetary gearset (4); a first gear shifting element (5); and a second gear shifting element (6), wherein the stepped planetary gearset (4) has at least a first ring gear (8 a), a second ring gear (8 b) and a plurality of stepped planet gears (10) rotatably mounted at a first planet carrier (9), wherein the first planet carrier (9) is configured to be drivingly connected to an electric machine (11), wherein the second ring gear (8 b) is connected to an output shaft (12) of the gear unit (3) so as to be fixed with respect to rotation relative to it, wherein the first gear shifting element (5) is configured to fix the first ring gear (8 a) relative to a housing (13) in a closed state, wherein the second gear shifting element (6) is configured to bring the stepped planetary gearset (4) into direct drive in a closed state, and wherein one of the two gear shifting elements (5, 6) is in the closed state for driving the output shaft (12) in rotation.
 2. The gear unit (3) according to claim 1, wherein the first gear shifting element (5) is configured as a positively engaging shifting element.
 3. The gear unit (3) according to claim 1, wherein the first gear shifting element (5) is configured as a frictionally engaging shifting element.
 4. The gear unit (3) according to claim 1, wherein the second gear shifting element (6) is configured as a positively engaging shifting element.
 5. The gear unit (3) according to claim 1, wherein the second gear shifting element (6) is configured as a frictionally engaging shifting element.
 6. The gear unit (3) according to claim 1, wherein the first and second gear shifting elements (5, 6) are configured jointly as a double shifting element (40).
 7. A powertrain (2) for an at least partially electrically driven vehicle (1), comprising: the gear unit (3) according to claim 1; an electric machine (11); and a differential (16) configured to drivingly connect the gear unit (3) to two driven shafts (18 a, 18 b) arranged coaxial to an output axis (17).
 8. The powertrain (2) according to claim 7, wherein the differential (16) is configured as bevel gear differential.
 9. The powertrain (2) according to claim 8, further comprising a planetary gear assembly (14) which is drivingly connected to the output shaft (12) of the gear unit (3) and has at least a first planetary gearset (15).
 10. The powertrain (2) according to claim 9, wherein the first planetary gear set (15) of the planetary gear assembly (14) has a first sun gear (20), a third ring gear (21) which is fixed with respect to the housing, and a plurality of planet gears (23) rotatably mounted at a second planet carrier (22), wherein the first sun gear (20) is connected to the second ring gear (8 b) of the gear unit (3) so as to be fixed with respect to rotation relative to it.
 11. The powertrain (2) according to claim 10, wherein a differential carrier (16 a) of the differential (16) is connected to the second planet carrier (22) of the planetary gear assembly (14) so as to be fixed with respect to rotation relative to it.
 12. The powertrain (2) according to claim 11, wherein the gear unit (3) and/or the differential (16) are/is arranged at least partially or completely spatially inside of a rotor (19) of the electric machine (11).
 13. The powertrain (2) according to claim 12, wherein at least a first transmission stage (24) is drivingly arranged between the output shaft (12) of the gear unit (3) and the differential (16).
 14. The powertrain (2) according to claim 7, wherein the differential (16) is configured as integral differential (25) which has a second planetary gearset (26) and a third planetary gearset (27), wherein each planetary gearset (26, 27) is drivingly connected to a respective driven shaft (18 a, 18 b), wherein a first output torque is transmittable to the first driven shaft (18 a) by the second planetary gearset (26), and wherein a supporting torque of the second planetary gearset (26) is convertible in the third planetary gearset (27) such that a second output torque corresponding to the first output torque is transmittable to the second driven shaft (18 b).
 15. The powertrain (2) according to claim 14, wherein the integral differential (25) and the first and second driven shafts (18 a, 18 b) are adapted to be arranged coaxial to an output axis (17) of the vehicle (1). 